Since a positive electrode active material of a lithium secondary battery is a very important element that determines performance, durability, and capacity of the battery, there is a trend to show indefatigable zeal in developing technology for reliably mass-producing the positive electrode active material according to the burgeoning demand for the secondary battery.
As one of the trends, there was an attempt to use, as a precursor of the positive electrode active material, a core-shell structured particle formed by stacking a shell layer on a core particle (Korea Patent Publication No. 2013-80565 published on Jul. 15, 2013). Since such a core-shell structured structure is advantageous for use in the positive electrode active material in that the core particle and the shell layer perform functions complementary to each other, the core-shell structure is highly rated.
Examples of major factors, which determine physical properties of a core-shell structured particle, are a composition, a size, a shape of a core particle, and a composition and thickness of a shell layer.
Conventionally, in order to form the foregoing core-shell structured particle, a simple coprecipitation reactor, which induces a rotation flow by using an impeller, has been used. An example of such a coprecipitation reactor is disclosed in Korea Patent No. 1062404 (registered on Aug. 30, 2011). Since the conventional impeller-typed coprecipitation reactor has a reaction space in a very large bulk shape, the conventional impeller-typed coprecipitation reactor has considerable difficulties in precisely controlling the foregoing major factors, and especially, continuously completing the core particle and the shell layer in one coprecipitation reactor. This means that it is to difficult to obtain a core-shell structured particle having a desired component and composition, and it is unsuitable to massively produce the core-shell structured particle through the conventional preparing method.